Originally used as a blogTV.com April Fool's prank when the company replaced the overused acronym, LOL, with the line "Oh the hilarity". The line caught the attention of the chatters and is now commonly used as a variation of lol, rofl, lmao, etc.

Chatters: "Why does everyone keep saying 'Oh the hilarity'?"
blogTV: "Oh the hilarity, you people are so naive..."